This patent application claims priority under 35 U.S.C. xc2xa7119 from Singapore Patent Application No. 9804259-1, filed Dec. 9, 1997, which is incorporated herein by reference for all purposes.
THIS INVENTION relates to a method of determining a clearance variation between a magnetic transducer and a magnetic recording medium during a track seeking operation.
Further, this invention relates to moving storage apparatus of the type in which a read/write transducer head supported on a slider is in contact with the storage medium when at rest and xe2x80x9cfliesxe2x80x9d above the medium surface when the medium is moving at operating speed, and more particularly to a method and apparatus for measuring the flying height of the transducer over the medium during track seeking operations. Experimental results have revealed a body of evidence that the track seeking operation causes loss/gain of head-disk clearance and sometimes results in slider-disk impact during the track seeking operation. This flying instability of the head may cause disk drive failure.
During track seeking operations, the seeking velocity, acceleration and deceleration are high and it is not easy to monitor the head-disk clearance variation with a conventional flying height tester which measures the head-disk clearance when the head is in a static position flying over the same track. It is difficult to study the influence that the track seeking operation has on flying height.
As the storage capacity of magnetic recording disks is increased by reducing track width, transition length and head-disk clearance, the heads must fly closer and closer to the recording surface in order to maintain adequate signal strength and to achieve a better signal-to-noise ratio. If the head contacts the recording surface while the disk is moving, the resultant xe2x80x9chead-disk crashxe2x80x9d can wipe out previously recorded data, cause weariness and head gimbal assembly (HGA) damage, damage the recording surface, and/or the slider surface on which the head is mounted.
Proximity recording technology is being used in disk drive design and has pushed head-disk clearances to a level of 0.6 to 1.2 xcexcin range. Furthermore, in proximity recording, the amount of contamination build-up on a slider surface and the slider""s flying performance are very sensitive to the assembly accuracy, air bearing surface design and dynamic performance of the head-gimbal assembly. Therefore, it is important to have a testing technique which can reveal the dynamic performance of the head-gimbal assembly (HGA) of a disk drive.
This invention provides a simple in-situ recording and testing technique for the measurement of head-disk clearance variation during the track seeking operation. The technique can be used easily, and the results can be used to characterise the dynamic performance of the HGA after assembly and also to characterise the performance of the track seeking process.
Known methods for measuring flying height have included various capacitive and optical techniques which require special xe2x80x9ctestxe2x80x9d disks or sliders. These methods are unable to measure the head-disk clearance in-situ or in a direct manner. The clearance between real sliders and disks is inferred from the measurements from the xe2x80x9ctestxe2x80x9d sliders or disks. These methods have been suitable up to the present. However, these methods lack the capability of in-situ measurement, especially at disk drive level.
U.S. Pat. No. 4,872,071 describes a method and apparatus for detecting abnormal operation of a magnetic disk file by reading data from a predetermined read-only area of each track. The amplitude of these readback signals is compared with the amplitude of similar signals readback from other tracks. If the comparison indicates a predetermined degree of variation, an alarm is given so that corrective action can be taken to avoid an impending head crash.
U.S. Pat. No. 4,777,544 describes another method and apparatus of incidental interest which uses the Wallace equation which expresses the dependence of readback voltage on various recording parameters including head/disk spacing and the use of a harmonic ratio flying height circuit to measure head/disk clearance in-situ. It is directed essentially to the measurement of the average flying height along a track, and the use of that information during the manufacture of the drive.
U.S. Pat. No. 5,130,866 describes a method and circuitry to sense the clearance between a magnetic transducer and recording medium by pre-writing magnetic transitions on a pre-selected area of the media and obtaining a readback signal therefrom. The pulse width of the readback signal is sensed at a pre-selected percentage of its base-to-peak amplitude. A voltage proportional to the width of the readback signal provides a measurement of the clearance.
So far, all existing techniques for head-disk clearance measurement are based on the reading operation of the system and assume that the flying height is the same during the writing operation.
No known techniques provide a simple and practical method of recording magnetically the spacing between a magnetic transducer and the recording medium in-situ in a direct manner at disk drive level during the track seeking operation.
It is, therefore, an object of the present invention to provide a method for measuring the clearance variation between a magnetic transducer and a recording medium in-situ in a direct manner in an operational magnetic disk storage system during track seeking operations.
Accordingly, one aspect of the present invention provides a method of determining a clearance variation between a magnetic transducer and a magnetic recording medium during a track seeking operation, the magnetic recording medium being moveable with respect to the transducer, which method comprises the steps of: at least partially erasing a predetermined area of the recording medium including at least one test track and one reference track; writing a series of predetermined magnetic transitions along a spiral trace formed by the read/write head during its track seeking across the predetermined area; reading the test track and obtaining, from the signals readback from the test tracks, the pulse width of the readback signal at a predetermined amplitude level; writing a further series of predetermined magnetic transitions identical to the first series on the reference tracks of the recording medium in the predetermined area; reading the reference track and obtaining, from the signals readback from the reference track, the pulse width of the readback signal at the predetermined amplitude level; and the pulse width difference being indicative of the clearance change caused by track seeking operations.
A further aspect of the present invention provides a method of determining a clearance between a magnetic transducer and a magnetic recording medium during a track seeking operation, the magnetic recording medium being moveable with respect to the transducer and including at least a test track and a reference track, which method comprises the steps of: pre-recording a series of predetermined magnetic transitions on a predetermined area of the recording medium including at least one test track and one reference track; at least partially erasing the magnetic transitions along the recorded tracks of the recording medium at a predetermined erasing current during track seeking across the predetermined area, the effect of the partial erasing being sensitive to changes of the head-disk clearance during track seeking; reading the test track and obtaining, from the signals readback from the test track, residual amplitude of a partially erased part of the test track; writing a reference track, obtaining the amplitude of the reference track, erasing the magnetic transitions on the reference track at the same predetermined partial erasing current; reading the reference track and obtaining, from the signals readback from the reference track, an average residual reference track amplitude; and comparing the residual amplitude from the partially erased part and the residual reference amplitude, said comparison being indicative of the change of the clearance between the magnetic transducer and the magnetic recording medium caused by track seeking operations.